Oil shale retorting



United States Patent O 3,384,569 GIL SHALE RETORTING Nick P. Peet, Houston, Tex., assigner to Esso Research and Engineering Company, a corporation of Delaware Filed Feb. 21, 1966, Ser. No. 529,094 9 Claims. (Cl. 208-11) ABSTRACT F THE DISCLOSURE In plural stage thermal retorting of crushed oil shale, lines are separately recovered from vertical preheating, retorting, burning and cooling zones through which the crushed oil shale serially flows, with the oil-free fines removed from the burning and cooling zones being discarded and the oil-rich fines removed from the preheating and retorting zones being introduced into the burning zone, ue gas from the burning zone being used to provide heat in the retorting zone by indirect heat exchange with preheated oil shale therein.

The present invention is directed to retorting of oil shale. More particularly, the invention is concerned with a method for retorting oil shale in which improved thermal eiciencies are achieved. In its more specific aspects, the invention is concerned with retorting oil shale in a plural stage thermal operation.

The present invention may be briey described as a method for retorting oil shale in a plural stage thermal operation in which shale oil is recovered from crushed oil shale. The plural stage comprises preheating, retorting, burning and cooling zones in which the crushed shale moves serially through the zones and in which shale fines, flue gas and shale oil are formed. In the method in accordance with the present invention, the shale fines are separately removed from each of the zones with the lines removed from the burning and cooling zones being substantially oil-free and discarded. The fines removed from the pre-heating and retorting zones are substantially oil-rich and are introduced into the burning Zone to provide a source of fuel. Also introduced into the burning zone is a free oxygen-containing gas such as air. The oil-rich lines may be admixed with the free oxygencontaining gas and the free oxygen-containing gas thus serves as a carrier for the oil-rich lines. Introduced into the retorting and cooling zones is a combustible gas, such as a high B.t.u. content gas, which is preferably separated from the shale oil in a later stage in the process, but which may originate outside the system. Natural gas may be used as the combustible gas having a high B.t.u. content. High B.t.u. content as used means a B.t.u. value of about 500 to about 2500. Preferably, a B.t.u. value for the gas may range from about 800 to about 1200 B.t.u. Gas from the cooling zone is introduced into the preheating zone as a preheating fluid while flue gas from the burning zone is introduced into the retorting zone into indirect heat exchange with oil shale therein. Shale oil is recovered from the preheating and retorting zone by virtue of an operation such as briefly described. High over-all thermal efficiency is achieved by recovery of heat, and carbonaceous material in the oil shale is slibstantially completely utilized in the operation.

The shale oil is recovered in vaporous form and cooled exteriorly of the preheating and retorting zones and thus is not available for recycling in the several stages which ordinarily in the prior art processes results in consumption of oil and lowering of yield.

The high B.t.u. gas is separated from the shale oil 4after cooling and condensing of the vaporous shale oil.

The fines removed from the preheating and retorting zones are separated from vaporous shale oil before be- ICC ing introduced into the burning zone, and the ines removed from the burning and cooling zones are separated from flue gas before being discarded. The ilue gas which is introduced into the retorting zone in indirect heat eX- change is Withdrawn from the retorting zone and may be discarded such as through a waste heat boiler for recovery of heat or may be reheated either in a separate vessel or other heating means and reintroduced for indirect heat exchange into the retorting zone.

As stated, the oil-rich fines may be introduced into the burning zone in admixture with the free oxygen-containing gas.

In the practice of the present invention, temperatures in the preheating zone may range from about 400 F. to about 800 F. with a suitable temperature being about 600 F. A hot gas at about 1000 F. may serve to preheat the fresh oil shale which may be introduced at `a temperature of about F.

Temperatures in the retorting zone may range from about 600 F. to about 1000 F. with a temperature suitably about 900 F. A high B.t.u. gas may be introduced into the retorting zone. The amount of the high B.t.u. content gas introduced into the retorting zone may Ibe range from about 5,000 to about 15,000 cu. ft. per ton of raw oil shale with about 10,000 cu. ft. of high B.t.u. content gas per ton of raw oil shale being satisfactory. The high B.t.u. gas may be preheated to temperatures up to l200 F.

In the burning zone, the temperature may range from about 1000 F. to about 1400" F. and suitably air at about 80 F. in an amount of about 3,000 to about 6,000 cu. ft. per ton of raw oil shale may be introduced, About 4,000 cu. ft. of air per ton of raw oil shale may be used. The air may be at about 80 F. Other free oxygen-containing gases having a greater content of free oxygen than air may be used.

Temperatures in the cooling zone may range from about l400 F. to about 200 F. with a high B.t.u. content gas being introduced thereinto for cooling purposes. Thus, the spent shale may enter the cooling zone at 1400 F. and may leave the cooling zone at 400 F. with about 12,000 to about 20,000 cu. ft. of the gas per ton of raw oil shale being used. About 18,000 cu. ft. of the high B.t.u. content gas per ton of raw oil shale may be satisfactory.

The pressure on the process may range substantially from atmospheric pressure to as high as 3000 p.s.i.g. A suitable pressure is about 15 p.s.i.g.

The present invention will be more fully described by reference to the drawing in which the single figure is a flow diagram of a preferred mode and embodiment.

Referring now to the drawing, numeral 11 indicates a charge line or conduit by way of which fresh crushed oil shale is introduced into the system from a source not shown. Line 11 leads into a preheat vessel or zone 12 provided with a distribution means or spider 13 connected to line 10 which introduces hot gas at a temperature of about l000 F. The oil shale and hot gas flow countercurrently to each other in zone 12 with the preheated shale discharging by line 14 into a vessel comprising a retorting zone 15.

The vaporous and gaseous materials from zone 12 are discharged by line 16 into a separator 17 which may suitably be a cyclone separator from whence the gaseous material and vaporous material may leave by line 18. The vaporous and gaseous materials in lines 16 and 18 are at a temperature of 250 F. and are therefore routed by line 19 containinga cooler-condenser 20 into a separator 21 wherein the condensed hydrocarbons shown as body 22 are separated from water 23 in leg 24 of separator 21, the water being discharged by line 25 and the hydrocarbons by line 26. High B.t.u. content gas is Withdrawn from separator 21 by line 27a part of which is recycled, in a manner which will be described, by line 28 while the remainder may be recovered by line 29 for further use as may be desired.

Returning now to the retorting zone 15, this zone is provided with internal tubes 27 for indirect heat exchange with the preheated shale owing downwardly through zone from zone 12. In zone 15, the preheated shale contacts the high B.t.u. content gas from line 29 Vwhich is introduced into retorting zone 15 by branch line 36 connecting to distribution means such as spider 31. The preheated shale in zone 15 is retorted by heat supplied indirectly to the internal tubes 27 by line 32 from a source, which will be described further, with the ue gas leaving the tubes 27 by line 33. This flue gas which is at a tem perature of about 700 F. may be reheated by circulation through a furnace or other heating means or by heat exchange with material in the process at a higher temperature. The flue gas introduced in line.32imay be at a temperature of about 1800" F. The shale after being retorted in zone 15 leaves zone 1S by line 34 and is iutroduced thereby into a vessel providing a burning zone 35. The retorted shale introduced into burning zone may be at a temperature of about 1000 F. and is contacted with a free oxygen-containing gas such as air introduced by line 36 at a temperature of about 80 F. from a source not shown through a distribution means such as spider 37. Admixed with the air in line 36 for introduction into line 3S are oil-rich fines recovered from preheating zone 12 in cyclone separator 17. These recovered oilrich fines are introduced into line 36 by line 38 which connects thereto.

The vaporous shale oil which may also be in the form of a mist with entrained liquid shale oil is withdrawn from zone 15 by line 39 and discharged at a temperature of 900 F. into separator 40 which may be a cyclone separator. The products separated from the fines in separator`40 are introduced by line 41 into branch line 19 for recovery of hydrocarbons and high B.t.u. gas as has been described. The oil-rich fines separated from the mist or vaporous shale oil are withdrawn from separator 40 by line 42 for introduction into line 36 in admixture with the air for ultimate injection into burning zone 35.

The spent shale from burning zone 35 is withdrawn by line 43 at a temperature of about l400 F., 'and introduced thereby into a vessel dening a cooling zone 44 into which there is introduced by line 28, which connects to distribution means such as spider 45, the high B.t.u. content gas recovered from separator 21.

The spent shale at a temperature of about 400 F. is

discharged by line 46 from the system.

The flue gas from burning zone 35 discharges by line 47 into a separator such as a cyclone 48 from whence the flue gas is withdrawn by line 32for use in zone 15 with the spent shale lines, being substantially oil-free, being discharged by line 49 from the system.

Likewise, the iiue gas from zone 44 is discharged by line 50 into a separator 51 which may be a cyclone separator from whence the gases by line 10 are introduced into Zone 12. Substantially oil-free fines are discharged from zone 51 from the system by lines 52.

Since the spent shale fines in lines 49 and 52 are at temperatures, respectively, of 1800 F; and l000 F., this material may be passed into heat exchange either with the the flue gas in line 33 or the fresh oil shale in line 11.

It will be seen from the foregoing description taken with the drawing that an el'licient thermal operation is described.

ln order to illustrate the invention further, oil shale crushed and screened to a 3/8 to 3" size range is fed countercurrently through a series of four vessels in the first of which the shale is preheated to a temperature of 600 F. by adsorption of heat from a recycle gas stream introduced into the bottom of the vessel at a temperature of l000 F. The recycle gas is removed from the top of CII the preheater vessel, passed through a cyclone for removal of shale fines, and mixed with the vapor product leaving the retorting vessel.

The preheated shale flows to the second vessel, in which retorting takes place. In the retort, the shale is heated to 900 F. by passage through externally heated vertical tubes of 8" diameter, Retorting takes place in the tube section and lower portion of the Vessel. High B.t.u. recycle gas is introduced into the bottom of the retort to provide a sweeping action for removal of the vapor products of retorting and to assist in transfer of heat from the Walls of the externally heated 8 tubes to the shale.

The oil and gas products from retorting plus the recycle gas are removed from the top of the retort in the vapor state and passed through a cyclone to remove shale lines, optionally through a waste heat boiler for recovery of heat, and then through a cooler-condenser. The effluent from the cooler-condenser is transferred to a separator where gas, oil and water are recovered as separate streams.

The shale leaving the retorting vessel ows downwardly into a burner vessel where residual carbonaceous material is burned. The hot iiue gas produced in the burner is conducted through a cyclone to remove shale fines and is then transferred to the tube section in the retorting vessel, heating the outside of the 8 tubes. The flue gas leaving the tube section is conducted to a stack and vented to the atmosphere. Indirect heating of the shale in the retort in this manner eliminates dilution of the hydrocarbons evolved with the liue gas produced by combustion of the residual carbonaceous material remaining on the retorted shale.

The shale flows from the burning vessel downwardly to the fourth or last vessel in the series. Recycle gas from the separator is injected into the bottom of this vessel and flows upwardly through the shale bed to recover heatffrom the shale. The heated gas leaves this vessel and passes through a cyclone to remove shale fines and is then injected into the first vessel of the series to preheat the shale. The cooled spent shale is rejected to a suitable spoils area. The shale fines recovered in the cyclone associated with the first and second vessels in the series contain carbonaceous material and therefore are injected into the air stream to the burner vessel where this material is burned providing additional fuel for the production of hot iiue gas. The spent shale fines from the lower two vessels are rejected to the spoils area.

Numerous advantages inure to a process as described herein among which are -removal of sale fines produced from each stage, preventing deleterious internal recycle of shale nes of the type experienced in single vessel processes. yMoreover, segregation and separate handling of gas streams used in each vessel results in a substantially lower gas quantity per ton of shale at any given point in the process as compared to a single vessel retort. Vertical retorts are gas-velocity limited and the present invention permits a substantial and important increase in throughput. By supplying heat for retorting through tube walls, the need for direct contact of the shale with large quantities of heat carrier steams is eliminated. In addition, high over-all thermal etiiciency is achieved by recovery of the heat from the spent shale to preheat the fresh shale charge and complete utilization of the residual carbonaceous material on the retorted shale as fuel in the operation is provided. Finally, removal of the gas and oil products in the retorting vessel in the vaporous state eliminates condensation of oil on cool, incoming shale as experienced in single vessel retorts. This prevents recycling of the oil and cracking and burning which results in a decrease in yield. Thus, the present invention is quite important and useful and represents in advance in the art of shale oil retorting.

While examples have been given of specific equipment and sizes of equipment, such as pipe diameters, it is to be understood that these Specic details are given by way of illustration and not by.way of limitation since larger or smaller sizes may be used, such as pipe diameters in the tube section in the indirect heat section of the retort from about 6 to about 20".

zones shale rines and gases and separating nes from said gases;

.separately removing from said preheating and retorting zones .shale lines and vapors containing shale oil and separating lines from said vapors;

the lines `removed from said burning and cooling zones being substantially oilfree and discarded;

the lines removed from said -preheating and retorting zones being substantially oil-rich and introduced into said burning zone;

introducing a free oxygencontaining gas into the burning zone;

introducing a combustible gas into the retorting and cooling zones as sweeping and cooling media, respectively;

introducing gas removed from said cooling zone Ias preheating fluid into .said preheating zone;

introducing the gas removed from said burning zone into said retorting zone into indirect heat exchange with the `oil shale to provide heat for retorting said oil shale -in said retorting zone; and

recovering shale oil from the vapors removed from said preheating and retorting zones.

2. A method in accord-ance with claim 1 in which the shale oil is recovered in vaporous form and cooled exteriorly of said preheating and retorting zones.

3. A method in accordance with claim 41 in which the combustible gas is separated from the shale oil recovered from at least sai-d retorting zone.

4. A method in accordance with claim 1 in which the combustible gas `is separated from the shale oil recovered from said -preheating and retorting zones.

5. A method in accordance with claim 1 in which the lines removed from preheating and retorting zones are separated from vaporous and gasiform material be'- fore being introduced into said burning zone.

6. A method in accordance with claim 1 in which the fines removed from said burning and cooling zones are separated from the gas in which they are suspended before being discarded.

7. A lmethod in accordance with claim 1 Iin Which the flue gas introduced into said retorting zone in indirect heat exchange is then withdrawn from said retorting zone, reheated, and reintroduced into said retorting zone in indirect heat exchange.

8. A method in accordance with claim 1 in which the flue gas introduced into said retorting zone in irldi'rect heat exchange is then withdrawn from said retorting zone, passed through a heat recovery zone, and discarded.

9. A method in accordance with claim 1 in which the oil-rich lines are introduced into said burning zone in admixture with said free oxygeircontaining gas.

References Cited UNITED STATES PATENTS 1,738,202 .l2/1929 Plantinga 201-29 1,796,100 3/1931 Heller 20L-l0 2,466,593 4/1949 Jones 20d-24 2,661,325 12/1953 Savage 201-'34 2,698,283 12/1954 Dalin 201-14 2,812,288 llt/1957 Lankford et al. 201--29 2,814,587 ll/l957 Van Dijck 208-11 FOREIGN PATENTS 894,727 4/ 1962 Great Britain.

DANIEL E. WYMAN, Primary Examiner.

P. E. KONOPKA, Assistant Examiner. 

